When Ajax technology is used extensively in complex web applications, debugging of such applications becomes a headache for developers, if they don't have the right tools for it. This is the where Firebug and FirePHP become handy. Firebug is an elegant, easy, and powerful add-on for Mozilla Firefox for debugging an Ajax-based application. It allows you to get a clear overview of Ajax requests, responses, and data sent to the server via the POST or GET methods. Furthermore, you can even edit the HTML and CSS code and preview the changes in real time, in the browser. Apart from this, Firebug also shows the entire HTTP request made by the web page. It also lets you profile JavaScript code. FirePHP is an extension of Firebug that extends the functionalities of Firebug by logging in information or messages on the Firebug console.